Turret mooring systems have been in use for some decades and as the search for hydrocarbons has increased, the depth from which hydrocarbons can be extracted has increased. The risers coming from greater depths are associated with greater loads and the turret wheel bearings now has to handle hundreds of tons. If the turret wheel bearing fails production must stop. Because of this it is desirable to maintain the turret wheel bearing while operating or minimize the length of the stoppage. Previous state of the art pretension systems comprise clamps or/and bolts pressing the rail segments against the support structure much like in rail way technology. The contact face between the adjacent rail segments will then be without compression stresses. Welded joints limit the selection of high strength materials which are required for these high loads.
The objective with using a rail comprised of rail segments is to                apply materials with very high strength uneasy to weld        limit the size of individual components        replace segments with the turret in place        
A very important feature is that the rail is getting a substantial compression stress by the pretension system. Advantages are:                1. contact between the rail segments remains in compression even at extreme radial turret loads        2. rail segments remain in stable position relative one to another thus avoiding fretting fatigue in the mating surfaces between adjacent rail segments        3. a high compression stress in the rail is advantages for the stress level in the contact zone between the wheel and the rail by the hydrostatic pressure effects        4. a rail subject to compression has a higher fatigue strength than without compression stresses.        5. the strength of the rail remains intact also in the rail joints 21.Re. 1. The compression in the rail is larger than the tangential stresses generated by the radial turret loads.Re. 2. The rail segments in the rail joints remain in relative vertical position due to the tongue and groove and due to the substantial clamping effects from the rail bolts 24.Re. 5. The strength of the rail in the edge of the material will be reduced. Generally, the contact pressure at the edge of a raceway for a roller bearing should generally be avoided or substantially reduced compared with pressure in the contact zone in the middle of the material. This is due to the hydrostatic effects obtained in the middle of the material, while at the edge there will be a tendency for the material to break away by the shear effect. By a substantial compression of the adjacent rail segments, it is obtained a rail joint where the neighboring rail segment are supporting each other. End face of the rail segment 42 is mutually supporting each other so that the combined effect will be close to the situation of an endless rail.        
KR 2015/0095361 A discloses a turret bearing supporting a turret in pool of a hull. The turret bearing comprises: a supporter mounted on the pool; a control bar installed in the supporter; a support plate moveably mounted to move from the supporter to the turret; and height adjustment means to move the support plate by means of the control bar.
WO 2015/123567 A1 describes a bearing assembly including a support ring, a plurality of bearing-element carrier members coupled to the support ring, and a plurality of superhard bearing elements having a lateral periphery extending between a base and a superhard bearing surface. At least one superhard bearing element of the plurality of superhard bearing elements is attached to each of the plurality of bearing-element carrier members. A bearing apparatus includes a rotor, a stator, and a bearing assembly. A method for assembling a bearing assembly includes attaching at least one superhard bearing element to each of a plurality of bearing-element carrier members and coupling the plurality of bearing-element carrier members to a support ring.
A rail system according to claim 1 and methods for mounting and replacing according to claims 10 and 11 helps to obtain the objectives and advantages mentioned above.